VBR versus CBR

[christopheramos]

Hi!

I am encoding an .avi file through CCE SP into MPEG-2 format, for later making it play on my standalone DVD player.

In CCE SP, I have the option of setting the output file to Constant Bit Rate or Variable Bit Rate.

I know from the glossary on this site that VBR is used mostly with files for DVD playing.

However, I get a better output when I encode at CBR rather than VBR.

My question is, if I encode it to CBR anyway, will this present a problem with my standalone DVD player? Or does the output file absolutely have to be in VBR?

Thanks!!!!!
Chris

[terjeber]

However, I get a better output when I encode at CBR rather than VBR.

This depends on the bitrate of your VBR encoding. If the movie piece you are encoding in some places have lots of movement and in others a lot less movement, VBR, for the same space, will typically give you better results over all than CBR. The reason you are seeing poorer results with VBR than CBR is probably that your average bitrate for VBR is quite low.

My question is, if I encode it to CBR anyway, will this present a problem with my standalone DVD player? Or does the output file absolutely have to be in VBR?

VBR or CBR doesn't matter to your DVD player at all. It will play both no problem.

[christopheramos]

Great!!! Thank you!!!!

[lenti_75]

if you encode higher than 6000 cbr or vbr is the same.

vbr is better for lower bitrates. I would encode it as vbr anyway, because when there is more action, it gets more bandwith.

[hanugro]

Which one is better? CBR @8kbps 1pass OR VBR set max,avrg,and min @8kbps (essentially cbr @8kbps) and 2pass?

[Cornucopia]

kbps?

Surely you mean Mbps.
8kbps will look like crap no matter what encoding method you choose.

At 8Mbps, the perceived benefits of 2pass VBR over 1pass CBR are VERY minimal (that IS getting quite close to the top of allowable DVD rates), so for speed reasons I would normally use the CBR there.

Scott

[christopheramos]

Cornucopia,

What are the top allowable DVD rates that you mentioned?

Right now I am encoding at 8,500 average; 8,000 minimum, and 9,000 maximum.

But I didn't know there was DVD rate limit???

Thanks!!

[redwudz]

From 'WHAT IS' DVD to the upper left:

Up to 9.8 Mbps* (9800 kbps*) MPEG2 video

Total:
Total bitrate including video, audio and subs can be max 10.08 Mbps (10080 kbps

Some players have no problem with the upper limit, some may have problems when you get too near to it.

[christopheramos]

redwudz,

Okay, so the total for DVD is 10.08 Mbps (or 10080 kbps).

I am compiling TV episodes onto a DVD. Can each episode be up 10.08 Mbps? Or must the total number of episodes (everything on the DVD) be 10.08 Mbps or less?

Right now, each of my episodes will probably come in at 8 or 9 Mbps. I don't know if that's going to be a problem or not.

Thanks!!!!

[Cornucopia]

Total for Each and Every title/chapter/cell/etc. is 10.08Mbps combined (Video+Audio+Subpicture/Subtitle+NAVIGATION)
Total per video stream (again each/every) is 9.8Mbps, .......just like it says.

Sounds like you shouldn't have trouble.

BTW, DVD players that have trouble above 8Mbps/9Mbps (but below the limit) are NOT COMPLIANT and should be returned. They're not even allowed to have the DVD-Video logo if they can't do that. It's mandatory in the spec. And, BTW, I've never used a player that ever had any problems, so they should be pretty rare.

Scott

[redwudz]

Those aren't hard and fast rules for the highest bitrate. But to be on the safe side, I try not to go above the 10000kbps number. Those numbers would apply to any and all files on the disc.

Pushing the bitrate too high is unlikely to give you much better of an encode. Generally, the visual difference between encoding at 8000kbps and 9000kbps is not that much and may not even be visible, even on a big screen.

If you are encoding this from a TV source, you could probably drop it down to 4000 and likely not see much difference. If your source is HDTV, then you might.

Why not just encode the same representative 5 minute or so clip at different bitrates and see what each looks like. That way you may be able to establish an optimum, not a maximum bitrate to use for the quality you want.

[christopheramos]

Well, I do encode for about 5 minutes to see, and can't tell a big difference. But that's on single pass VBR setting in CCE SP.

Right now I am encoding with 2 pass VBR, hoping the outcome will be a little bit better. But I have to wait until both passes are done in order to tell (a wonderful 7 hour wait).

With CCE, I can input a Minimum, Average and Maximum bitrate. But I don't see where it allows me to enter an "optimum" bitrate.

I have a bitrate calculator (Vcalc). I am not sure if that will tell me what is "optimal" or not. And if it does, I wouldn't be sure how to plug into into CCE's Minimum, Average or Maximum settings.

Does that make sense?

Thanks!
Chris

[jagabo]

No calculator can tell what bitrate is "optimal". The bitrate required for any particular video for any particular quality varies.

Use a constant quality encoder if you want "optimal" bitrates. The encoder will give you whatever bitrate is required do deliver the quality you specified.

[christopheramos]

jagabo,

Thanks. That would explain why I set CCE to about 8,500 kbps, but it actually encodes at about 5,570 kbps average.

Thanks!